Adjusting a bicycle derailleur — step-by-step guide

Why does a derailleur go out of tune?

Three main causes: first, the shift cable stretches in the weeks after installation — that's normal and almost always leads to the first re-adjustment. Second, the derailleur hanger (the small aluminium adapter between frame and derailleur) can bend through a crash, a tip-over or simply during transport. Third, chain and cogs wear over time to the point where indexing no longer catches — then no adjustment helps, only replacement. More in our guide Replacing a bicycle chain.

Tools you'll need

• Workstand (or a helper who holds the rear wheel up)
• 4 / 5 mm Allen keys
• Small Phillips or flat-blade screwdriver for the limit screws
• Optional: derailleur hanger alignment tool (or bring it to the workshop)
• A bit of patience — adjustment happens in small increments

Step by step: adjusting the rear derailleur

1. 1. Preparation & diagnosis

   Bike in the workstand, largest gear (smallest cog at the rear). Turn the crank and check: does the chain skip, rub on the derailleur, rattle? Check the derailleur hanger for bending — a view from behind reveals a crooked cage. If the hanger is bent, no adjustment will help — it needs to be aligned or replaced.

2. 2. H limit screw (highest gear)

   Shift to the smallest cog. The H screw on the derailleur limits how far outward the derailleur travels. Turn it so the pulleys sit exactly under the smallest cog — not further out, or the chain drops off. Screwing in = derailleur moves inward, out = outward.

3. 3. L limit screw (lowest gear)

   Shift to the largest cog (note: release cable tension first, otherwise it won't shift). The L screw limits the derailleur on the inside. Set it so the pulleys sit under the largest cog — not further in, or the chain can jump into the spokes. This is safety-critical.

4. 4. Cable tension at the shifter

   Back to the smallest cog. Tighten the shift cable at the derailleur clamp bolt — snug, not overtight. Now shift up one gear: the chain should climb cleanly onto the next cog. If it hesitates, increase tension (turn the barrel adjuster on the derailleur or shifter counter-clockwise). If it overshifts, reduce tension.

5. 5. B-screw (body tension)

   Shift to the largest cog. The gap between the upper pulley and the cog should be 5–6 mm. Too close = clattering shifts, too far = imprecise. Screwing the B-screw in increases the gap. On Shimano 12-speed and large cassettes, set exactly to manufacturer spec.

6. 6. Front derailleur (multiple chainrings)

   Height: the outer cage sits 1–3 mm above the largest chainring. Align parallel to the chainring. The H screw on the front derailleur limits outward (big ring), the L screw inward (small ring). Cable tension as with the rear derailleur. 1× drivetrains (no front derailleur) skip this step.

7. 7. Fine-tuning under load

   Test ride under load — shift up and down through all gears. Noises under load shifts show where to re-tune. On electronic groupsets (Shimano Di2, SRAM AXS), fine-tuning happens via a button on the shifter or in the app — the mechanics remain identical.

When to go to the workshop?

There are clear cases where DIY reaches its limits: bent derailleur hanger, worn cassette, defective shift cable, or an electronic system (Shimano Di2, SRAM AXS, Rohloff E-14) that no longer plays with the software. Also, if after 15 minutes of adjusting you can't get a clean shift, something bigger is usually wrong. In the workshop we have the right specialist tools — from a hanger alignment gauge to a Di2 diagnostic unit.

What does derailleur adjustment cost at our shop?

More details on the workshop page Derailleur adjustment.